To reduce energy costs and to improve water quality, water hyacinths and other plants have been introduced into wastewater holding ponds at a number of sewage treatment facilities in Florida. Once harvested the plants can be used for animal feed or biomass for energy production. The number of wastewater/aquatic-plant system is increasing rapidly throughout the southern portion of the United States. Unfortunately, mosquito problems emanating from these systems represent a major obstacle to the successful and widespread implementation of an otherwise sound approach for improving water quality and for conserving and producing energy. The proposed studies will determine how certain factors either enhance or reduce the abundance of mosquito egg rafts in wastewater ponds, especially those containing aquatic plants. Field study sites will include aquatic systems in subtropical and temperate zone regions of Florida where we will monitor on a year-round basis the density of egg rafts of the following species: Culex nigripalpus, C. quinquefasciatus and C. salinarius. These pestiferous, disease-vectoring mosquitoes are abundant in some wastewater/aquatic-plant systems, but not in others. To account for these differences, we will investigate the effects of the following on ovipositional activity: (1) water quality, (2) the degree and kind of plant cover and (3) variations in abundance and flight behavior of adult mosquitoes. In much of southeastern United States, C. quinquefasciatus populations are in an active growth phase during the Spring, Summer and Fall with peak abundance normally occurring during summer. However, in peninsular Florida this species is least abundant during the Summer and Fall. This paucity of C. quinquefasciatus has been attributed to the heavy rains which usually fall during this period and apparently dilute and carry off nutrient-rich waters; thus eliminating the mosquito's habitat. Our experiments will test this and other hypotheses concerning seasonal and geographical variations in the relative abundance of Culex mosquitoes. The data derived from this study should provide a basis for the development of better wastewater/aquatic-plant systems which minimize public health and environmental hazards, while retaining economically desirable features.